1. Field of the Invention
The present invention relates to water dispensers including refrigerated and non-refrigerated water dispensers that provide a reservoir for holding water. More particularly, the present invention provides an improved method and apparatus for sanitizing drinking water to be dispensed from a water dispenser having a reservoir wherein ozone gas is generated and transmitted from a generator to the water dispenser reservoir, a pump being positioned inside the reservoir that enables the ozone gas mechanically broken up inside the reservoir to produce very small ozone gas bubbles that are used to disinfect the water in the reservoir and the reservoir floor.
2. General Background of the Invention
The EPA publication “Alternative Method's of Disinfection” relates that aerator diffusion systems have achieved over 95% ozone mass transfer diffusion efficiency when properly configured. The highest transfer efficiencies are achieved by any known conventional means used in large scale ozone water treatment applications.
Aerators are special types of liquid pumps adapted to production of a mixed phase gas and liquid flow stream for the sole purpose of dissolving said gases into the liquid. Two types of conventional aerator pumps can be used for adaptation to the batch type water dispenser reservoir as the primary ozone diffusion means. The two conventional types are high shear centrifugal flow aerators as described for example by the Naito, U.S. Pat. No. 4,193,949, hereby incorporated herein by reference.
A centrifugal water pump impeller designed for aeration, as the name implies, pumps liquids by radial action of radial or spiral blades or tines. Such blades or tines are either sandwiched between two discs or affixed to a single disc. In most instances they act as a housing where water and a gas are draw in from either ports located near the axis or in the case of the single disc types open to the bulk liquid. This fluid is propelled radially outward by the radial-centrifugal pushing and slinging action of the plurality of vanes in rotary motion. Gas is typically supplied through ports in a hollow drive shaft or in the case of single disc open impeller models, from an annular opening formed between shaft and exterior sleeve in connecting with gas supply. In some models, the perimeter of the dual disc radial flow impeller is provided with a housing displaying a plurality of slots or a screen capable of further sub-dividing gas bubbles by shear between porous perimeter housing surface and tips of the blades and passage through the metered slots or screens.
Axial flow impellers pump water sourced from an axial suppling means through one or more pitched rotary screw impellers. These screw impellers propel water axially by pushing and form a region of low pressure on the water intake side, providing the means for gas siphoning to the liquid for shear mixing by the impeller. Variations range from thin dimension, low pitched shearing blades with one or more such impellers like those found on vortex action household blenders. These devices aerate and mix gases from the air gap with the liquid such as disclosed by Zeff, U.S. Pat. No. 3,843,521, hereby incorporated herein by reference. The Zeff '521 patented pump uses an impeller stack consisting of one or more high pitch drive impellers that pump water and provide maximum gas siphoning rates when stack is placed in a tubular housing. The most advanced stack models exhibit thin walled parabolic cross-sectioned net-zero pitched shearing blades lying between drive impellers that generate maximum turbulence and regions of high and low pressure within the flow stream capable of shearing a partial mixed gas phase down to fast dissolving non-buoyant, gas colloid-suspension dimensions.
Due to their increased gas siphoning ability without adverse gas flooding cavitation to impellers resulting in liquid flow stoppage, such pumps are often outfitted with positive pressure gas supplies capable of quickly gas saturating liquids.
Gas bubble volume to water mass transfer in open cooler reservoir systems with tuned aerator pumps can rotary shear gas bubbles down to micron dimensions found in pressured water venturi injection systems. Gas being a compressible fluid, when the venturi injection returns ozonated water flow to open systems cooler reservoir with corresponding pressure decrease, bubbles quickly increase to larger dimensions that quickly rise to reservoir air water interface and exhaust without effectively mass transferring any of the prossess ozone to water in the highly abbreviated water columns of cooler reservoirs.
Typically, low pressure, fine bubble diffuser stones are limited to production of bubbles no smaller than about 300 micron diameters with the majority of the bubble population capable of supporting adequate gas volumes for disinfecting reservoirs in contacting times ranging from 10-45 minutes with small output ozonators lie in the 400-600 micron diameter range, relatively slow rising and exhausting bubbles.
Diffusion efficiencies of cooler based diffuser stone based diffusion typically do not exceed 5-40% depending on ozonator output. Gas supply rates cannot exceed 2 liters per minute in the most prevalent 2 liter water volume form of cooler without turning the reservoir water volume to froth with the accompanying risk of inducing catastrophic cooler flooding in bottled water coolers and float regulated pressured supply point of use coolers.
When a point of use type water dispenser intake valve float drops due to loss of liquid head and allow pressured supply to continuously dump water into reservoir that in turn is continually converted to low density froth. Flooding can occur in these devices from overdriven ozone supply systems.
All of these deficiencies can be overcome with air flow rate and bubble size tuned aerator systems that are capable of circulating chiefly non-buoyant bubbles around in the reservoir and inhibiting the buoyant bubble size fractions from rising to the surface, exhausting with a swirling flow circulating around reservoir walls instead of toroidal water flow dynamics that roll to air water interface and back down. In effect, this feature greatly increases the contacting times of the larger bubble fractions. The very small non-buoyant fractions diffuse by pressure dynamics, diffusing to extinction in usually about 40 seconds are less. The larger buoyant fraction on the other hand must be diffused by the conventional motional transfer of external bubble film mixed phase gas-water stripping dynamics.
In cooler reservoir bubble reactors, the conventional method has not demonstrated itself to be an effective transfer means for low bubble rise velocity in abbreviated water column. Layer stripping diffusion of this bubble fraction requires considerable mechanical stirring action, as occurs with aerator circulation where the layer is stripped and contents dispersed within the bulk liquid by active mixing, decreasing gas solution density around bubble allowing the mixed phase layer to quickly replenish and be stripped again in a low dissolved gas environment. With continual stripping of bubbles whose initial size was 500-700 microns, bubble sizes diminish until they reach non-buoyant, fast pressure diffusion bubble dimension where viscous drag and circulation in excess of rise velocity holds these bubbles in suspension until they diffuse to extinction. This effect has been demonstrated with sparingly soluble ozone and air dissolving in water at water temperatures in excess of 75 F with aerator diffusion.
The rapid mass transfer effect is only accelerated in chilled water found in cooler reservoirs averaging about 38 degrees F. It is not uncommon in 2 liter chilled water volumes to gas saturate the water in less than about 4 minutes to the point continued aeration is a pointless waste of energy. Site generated ozone as dissolved ozone concentration peaks long before the remaining gas phase stored in small non-buoyant bubbles have depleted. The dissolved gas concentration effectively inhibits further gas transfer to the liquid. On return to static equilibrium conditions, post aerator diffusion, the reservoir water volume begins to demonstrate the milky liquid light dispersion appearance of a true, meta-stable gas colloid that will remain stable for days without off-gassing and returning to a clear state.
Due to the effectiveness of rotary mechanical shearing of gas to fine particulate dimensions and circulation capture of gas particles that one can achieve with aerator diffusion, aerators or their impellers can be located either near the reservoir air-water interface or (when operating near the bottoms of coolers) provided with a small water intake extension in addition to regular intake whose terminus lies relatively close to the interface to form a vortex capable of drawing exhaust phase ozone back down into the water where it can be recycled and transferred to water, reducing process ozone demand even further.
As long as the amount of exhaust gas quantity drawn into the mixer is small, the effect on primary process ozone siphoning is small and impeller cavitation will not occur. A further consideration is keeping ancillary extension's intake orifice small to eliminate the potential the reservoir flooding resulting from the formation of large vortices.
Another option open to axial flow housed impeller stack aerators, that of split flow transfer of ozonated water to other regions of a cooler include the ability to pump ozonated water from reservoir into water bottles of bottled water coolers. This results in pre-ozonating the source water and sanitizing the inner surfaces of bottles as well as its anti-spill device, the tubular hypodermic like protusions that pierce special sanitary bottle caps. When bottled water and especially the tubes of anti-spill devices extend up into the clear bottles exposure to sunlight over extended periods causes algae to bloom in the bottle. This forms algal biofilms on both bottle and tubular extension surfaces that ozonated water will bleach and render inert. Since there is little air exchange associated suspended fine bubbles and dissolved ozone, the positive displacement ozonated water pumped into bottles, returning to reservoir by gravity flow at a rate equal to that pumped in, thus no danger of the disequilibria, air exchange cooler flooding exists.
Prior art addressing ozonating water in the bottle, is seen in the Troglione, U.S. Pat. No. 3,726,404. The '404 patent reveals a dual reservoir transfer ozonation system, usable to disinfect a bottled water dispenser=s water. The primary differences in the '404 patent as opposed to the present embodiment are that Troglione required a dedicated water pump to pump water from a separate ozone bubble reactor reservoir reserve to the bottle and demonstrated no capacity to completely exchange the non-ozonated contents of the bottle with freshly ozonated reservoir water. Troglione '404 required a dedicated air pump for transferring ozone to the bubble reactor>s porous diffuser stone. The present invention provides other split-flow transfer options include running small diameter tubing through water courses that terminate immediately behind spigot valves for back flushing watercourses and exposed valve bodies with freshly ozonated water, thereby bleaching and washing any biofilms that might have formed in these stagnate, slow water mixing exchange areas. Such areas would not otherwise be exposed to high concentrations ozone unless freshly ozonated water were dispensed from cooler, which represents insufficient contacting time without sufficient water flow velocity to achieve a biofilm abrading effect. The bleaching and scrubbing of organic deposits with rising streams of ozone bubbles aimed at reservoir sidewalls by a gated ring diffuser is discussed in the Davis U.S. Pat. Nos. 6,085,540 and 6,389,690 for reservoir sidewall sanitisation.
Removal and bleaching of the reservoir floor or bottom wall area is most necessary as the loose sediment has no place to go except down the watercourses and out the spigot into an individuals drinking glass. In fact no other conventional form of diffusion presently in use can provide the stirring action and accompanying turbulence need to stir up sediment and strip biofilms from a reservoir base and beach them to an inert.
Small applications aerators of appropriate scale for cooler applications can be supplied by current manufacturers in two basic configurations: Firstly, in compact, short shafted units in housing's integrated with its prime mover suitable for below water level in reservoir mounting, inversion mount with only impeller stack and housing protruding through reservoir base or 90 degree sidewall mount, impeller and housing protruding through reservoir sidewall. In the case of a cooler reservoir outfitted with two tangential sidewall ports connected to supply tubing, one side serves as water inlet, the other as a water outlet with a mixing chamber located between the two terminal ends of tubing. An aerator is fixed to the external mixing chamber where water can be pumped, and shear mixed and siphoned ozone supply from ozonator can be siphoned across impeller, shear mixed and pumped into reservoir flowing in the preferred swirl around the reservoir perimeter. Ozone can be recycled through the aerator, with or without split stream transfer to the previously described critical areas.
Long hollow gas supply drive shafted units are suitable for exterior motor mounting to a point of use (POU) cooler reservoir cover or to the anti-spill device cover found on bottled water coolers where impellers and the associated housing project into the reservoir below water level.
Silva U.S. Pat. No. 3,382,980 discloses a radial flow aerator being used as primary ozone diffusion means in an on demand, partially continuous throughput water treatment system suitable for the needs of small municipalities. The reservoir was built expressly for this purpose. The Silva system has a dual reservoir, contactor separate form dispensing accumulation tank and water is not chilled in either tank and not the same utility.
Blender impellers (see e.g. Zeff U.S. Pat. No. 3,843,521) are of the axial flow type, but differ from chemical engineering gas diffusion aerators in that the chemical engineering models feature housed impellers and gas tube supplying means and flow directed mixed phase flows that minimize or eliminate vortex and corresponding air core conduits from surface. The open impeller design of blenders in conjunction with the container geometry incorporated by Zeff cause cyclonic toroidal convection vortex flow in the aerator embodiment due to the potential of cooler flooding. The low density air core of a vortex can destabilize both a bottled water cooler and a float actuated point of use cooler's water supplying means, promoting uninterrupted water drainage into the cooler reservoir. This type of axial aerator is incapable of directing split flow streams to other parts of a cooler.
Several patents have issued that discuss the general concept of using ozone to sanitize drinking water contained in the reservoir of a water dispensing device, water cooler, or the like.
As examples, patents have issued that relate to the use of ozone for disinfecting drinking water that is to be dispensed. U.S. Pat. Nos. 6,085,540 entitled “Method and apparatus for disinfecting a water cooler reservoir”; 6,389,690 entitled “Method and apparatus for disinfecting a water cooler reservoir”; 6,532,760 entitled “Method and apparatus for disinfecting a water cooler reservoir”; 6,561,382 entitled “Method and apparatus for disinfecting a water cooler reservoir and its dispensing spigot(s)”, each of said patents being incorporated herein by reference.
Other possibly relevant patents include Olsen U.S. Pat. No. 5,683,576 and Matsui U.S. Pat. No. 5,366,619.